Crosslaminate of oriented films and methods and apparatus for manufacturing same

Abstract

A crosslaminate is formed from two oriented plies of thermoplastic polymer material, arranged so that their orientation directions cross one another, the plies being heat sealed together. Each ply is semi-fibrillated, that is consist of linear thin regions of biaxially oriented material and thicker linear bosses between the thinner regions. The webs are sealed primarily through bonds formed at the intersection of the bosses (thicker regions). The array of bosses has a division less than 2 mm. The laminate has improved aesthetic and strength properties. A method for forming the crosslaminate involves segmental stretching of the material to form the thinner regions, and apparatus comprising intermeshing grooved stretching rollers having sharp-edged crests is described.

I claim: 
     
       1. A method of manufacturing a crosslaminate comprising the steps of:
 segmentally stretching a first ply by passing the first ply through a first pair of grooved rollers with flat crests to form a first array of thicker and thinner linear bosses distributed over the first ply with a division between adjacent linear bosses of no larger than about 2 mm, where the linear bosses of the first array are integrally connected by thinner linear webs, where each web, by volume, is less than 50% of an average volume of two adjacent bosses and where a delineation between a boss and an adjacent thin region comprises a location where a ply thickness is an average between a thickest part of the boss and a thinnest part of the web; 
 segmentally stretching a second ply by passing the second ply through a second pair of grooved rollers to form a second array of thicker and thinner linear bosses distributed over the second ply, where the linear bosses of the second array are integrally connected by thinner linear webs; 
 laminating the first ply to the second ply by bonding thicker linear bosses of the first ply to thicker linear bosses of the second ply without bonding the thinner linear bosses or the thinner linear webs of the first ply to the second ply and without bonding the thinner linear bosses or the thinner linear webs of the second ply to the first ply, wherein when laminated a predominate direction of orientation of the first ply is at an angle to a predominate direction of orientation of the second ply and the first array of thicker and thinner linear bosses extend in a direction perpendicular to the second array of thicker and thinner linear bosses. 
 
     
     
       2. The method according to  claim 1 , further comprising the step of: prior to the laminating step, longitudinally stretching the first ply in a substantially uniaxial manner. 
     
     
       3. The method according to  claim 1 , further comprising the step of: prior to the laminating step, longitudinally stretching each of the first and second plies in a substantially uniaxial manner. 
     
     
       4. The method according to  claim 1 , wherein the flat crests each have two edges, each edge having a radius of curvature in the range 20 to 50 μm. 
     
     
       5. The method according to  claim 1 , wherein the two edges of each crest protrude farther than the rest of the crest. 
     
     
       6. The method according to  claim 5 , wherein the first pair of grooved rollers are heated to a temperatures between about 60° C. and 80° C., while the first ply is fed onto the rollers at a lower temperature between about 35° C. and 40° C. to selectively heat the first ply at portions that contact the two edges of the crests of the first pair of grooved rollers. 
     
     
       7. The method according to  claim 4 , wherein a pitch of the first pair of grooved rollers is less than 5 mm, and a distance from one to the other of the two edges on the crest is between about 0.3-0.5 mm, and a radius of curvature of the edges is in the range 20 to 50 μm. 
     
     
       8. The method according to  claim 4 , wherein segmental stretching the first ply comprises transversely stretching the first ply between the first pair of grooved rollers, where prior or subsequently to this segmental stretching, the method comprises segmental stretching the first ply between a third pair of grooved rollers, where the third pair of grooved rollers:
 a) produce only one stretching zone on each crest, 
 b) have a pitch the same as the first pair of grooved rollers, and 
 c) are in registration with the first pair of grooved rollers such that each stretching zone formed by the third pair of grooved rollers falls between or joins with the stretching zones formed on the edges of the first pair of grooved rollers. 
 
     
     
       9. The method according to  claim 1 , wherein laminating the first ply to the second ply comprises passing the first ply and the second ply together through a fourth pair of grooved rollers. 
     
     
       10. The method according to  claim 9 , wherein a first roller of the fourth pair of grooved rollers has axially extending crests and a second roller of the fourth pair of grooved rollers has radially extending crests. 
     
     
       11. The method according to  claim 1 , further comprising extruding a bonding layer in one or more of the first ply and the second ply. 
     
     
       12. The method according to  claim 11 , wherein a pattern of bonding in spots or linear regions is achieved by coextruding the bonding layer in the first ply and the second ply in form of an array of closely spaced narrow strips, whereby the strips in the first ply form an angle to the strips in the second ply, wherein laminating the first ply to the second ply comprises using a temperature and pressure adapted such that within each spot or linear region, the first ply and the second ply either become evenly bonded to each other all over, or become bonded to each other in a pattern of bonding/no bonding or stronger bonding/weaker bonding, corresponding to the pattern of bosses/thinner webs, while the remainder of the laminate is maintained unbonded or more weakly bonded than the average bonding within the spots or linear regions, referring to peel testing at 20° C. 
     
     
       13. The method according to  claim 1 , wherein a degree of uniaxial orientation in the bosses of the first and second arrays of thicker and thinner linear bosses is such that during slow tear propagation in the crosslaminate each of the first and second plies reorients instead of fibrillating in the location where the tear propagates. 
     
     
       14. The method according to  claim 1 , wherein laminating the first ply to the second ply comprises laminating using heat and wherein during or following the lamination of the first ply to the second ply, the shrinks along at least one of the main directions of orientation. 
     
     
       15. The method according to  claim 14 , further comprising selectively stabilizing the thinner webs in one or more of the first ply and the second ply by heating the thinner webs with hot air while the bosses are maintained at a lower temperature by contact with a cooled surface. 
     
     
       16. The method according to  claim 15 , further comprising removing slacks formed in the crosslaminate by heating with hot air while cooling the remainder of the crosslaminate by contacting the crosslaminate with a cooled roller. 
     
     
       17. The method according to  claim 1 , further comprising supplying the first ply and/or the second ply with an admixture of a suitable powder such that microvoids are formed during incremental stretching that pierce the thinner webs to make the crosslaminate breathable. 
     
     
       18. The method according to  claim 1 , wherein the first ply and the second ply comprise polyethylene. 
     
     
       19. The method according to  claim 1 , wherein laminating the first ply to the second ply comprises passing the first and second plies together through a fourth pair of grooved rollers having a first roller with a first diameter and a second roller with a second smaller diameter. 
     
     
       20. The method according to  claim 11 , wherein the bonding layer is selected as a blend of two or more compatible polymers of different melting ranges. 
     
     
       21. A method of creating a laminate film comprising:
 passing a first ply of thermoplastic polymer material having a dominating direction of orientation in a longitudinal direction through a first pair of heated grooved rollers to incrementally stretch the first ply in a transverse direction and create biaxially oriented thinner webs and first and second sets of uniaxially oriented bosses, the first set of bosses having a first thickness and the second set of bosses having a second thickness that is greater than the first thickness; 
 wherein each crest on the grooved surfaces of the grooved rollers has two edges, each of which has a radius of curvature in the range 20 to 50 μm; and 
 bonding a second ply of thermoplastic material to the first ply by bonding the bosses having the second thickness of the first ply to the second ply without bonding the bosses having the first thickness of the first ply to the second ply and without bonding the thinner webs of the first ply to the second ply. 
 
     
     
       22. The method according to  claim 21 , wherein the two edges protrude farther than the rest of the crest to limit the contact between the first ply and the grooved rollers to the edge portions of the crests. 
     
     
       23. The method according to  claim 22 , wherein the grooved rollers are heated to a temperature between 60° C. and 80° C. 
     
     
       24. The method according to  claim 21 , wherein a pitch of the grooved rollers is less than 5 mm, and the distance from one to the other of the two edges on the crest is between 0.3-0.5 mm. 
     
     
       25. The method according to  claim 21 , wherein bonding the second ply of thermoplastic material to the first ply comprises passing the first ply and the second ply together through a second pair of rollers.